Re: [IPsec] Garage door - let's pick a different example

[Yaron Sheffer <[e-mail]>]

On 07/26/2014 02:07 AM, Tero Kivinen wrote:
> Yaron Sheffer writes:
>> This might sound like a nit, but we have this text in the draft, as
>> a use case for null auth:
>>
>> "User wants to get some simple action from the remote device. Consider garage
>> door opener: it must authenticate user to open the door, but it is not
>> necessary for the user to authenticate the door opener.  In this case one-way
>> authentication is sufficient."
>>
>> The problem is, this is an incorrect protocol. Specifically, a MITM (who might
>> be physically located by the kitchen door), could redirect the protocol
>> exchange to a door different from the one I intended to open. Seeing that
>> nothing happens, I will simply press the remote again and open the garage
>> door, too.
>>
>> This is of course a generic problem, where unauthenticated protocols have
>> unforeseen consequences.
>
> No, that is not caused by the unauthenticated protocol, but caused by
> the same device to be used with two different doors. Even if the
> device would do full authentication and would verify that the door is
> in his list of doors which can be opened, attacker could still do the
> same thing.
>
> Only way to get rid of that, would be to either put display on the
> device telling which door responded, or put multiple buttons to the
> device and you would have to bind each button to exactly one door
> (i.e. each button using separate key or shared secret).
>
> And, not you do not even need man in the middle in cryptographic
> sense, just rerouting the packets from the air to the other
> destination would be enough.
>
> So for that kind of uses the device would need to be tied to exactly
> one door...
>

What you're saying is that to secure this system, we need authentication 
of the device, either at the IKE level or at the application level (plus 
UI improvements). I agree, and suggest again that this is not a good use 
case for null or one-way authentication.

Thanks,
	Yaron